The aqua iron(IV) complex, Fe(H2O)5O2+, is generated in acidic aqueous solutions from Fe(H2O)62+ and ozone. Fe(H2O)5O2+is a potent oxidant that reacts with organic and inorganic substrates by both one-electron and two-electron mechanisms. The oxidation of alcohols, for example, utilizes parallel hydrogen atom (1-electron) and hydride(2-electron) transfers. Oxygen atom acceptors, such as sulfoxides, react exclusively by oxygen atom transfer that regenerates Fe(H2O)62+. This reaction is one of the key steps in Fe(H2O)62+-catalyzed oxidations with ozone. Coordinating anions and/or decreased acidity alter the nature of Fe(IV) and cause major mechanistic changes in reactions that form and/or consume Fe(IV). Most notably, the reactive intermediate in Fe(H2O)62+/H2O2 (Fenton) reaction features Fe(IV) as the reactive intermediate at pH≥6, in contrast to the one-electron chemistry that involves hydroxyl radicals under acidic conditions.
Acknowledgement: This manuscript has been authored under Contract No. DE-AC02-07CH11358 with the U. S. Department of Energy.